Computers utilized in modern office environments are typically coupled to a local area network (LAN). The LAN allow users of the computers to share common resources, such as a common printer included in the network, and allows the users to share information files, such as by including one or more file servers in the network. In addition, the users are typically able to communicate information with each other through electronic messaging. A commonly utilized type of LAN is Ethernet. Currently, a variety of products which support Ethernet are commercially available from a variety of sources. Other types of LANs are also utilized, such as token ring, fiber distributed data interface (FDDI) or asynchronous transfer mode (ATM).
LANs are often connected to a wide area network (WAN) via a telephone modem. Thus, information is communicated over the WAN via a communication link provided by a telephone service provider. These telephone links, however, are generally designed to have a bandwidth that is sufficient for voice communication. As such, the rate at which information can be communicated over these telephone links is limited. As computers and computer applications become more sophisticated, however, they tend to generate and process increasingly large amounts of data to be communicated. For example, the communication of computer graphics generally requires a large amount of bandwidth relative to voice communication. Thus, the telephone link can become a data communication bottleneck.
Business organizations and their affiliates are often spread over several sites in a metropolitan or geographical area. For example, a business organization can have a headquarters, one or more branch offices, and various other facilities. For such business organizations, LANs located at the various sites will generally need to communicate information with each other. Wireless communication links for connecting local area networks are known. For example, U.S. Pat. No. 4,876,742, entitled “Apparatus and Method for Providing a Wireless Link Between Two Area Network Systems,” and U.S. Pat. No. 5,436,902, entitled “Ethernet Extender,” each disclose a wireless communication link for connecting LANs.
Availability is a measure of the average number of errors which occur in digitally transmitted data. An availability of 99.99 percent is commonly required for radio communications. For an availability of 99.99 percent, the average error rate for digitally communicated data must be maintained below 1×10−6 errors per bit, 99.99 percent of the time. The integrity of a wireless communication link, however, is largely dependent upon transient environmental conditions, such as precipitation. Environmental precipitation causes a severe attenuation of the transmitted signal. For example, to maintain an availability of 99.99 in the presence of environmental precipitation, the signal must be transmitted at a level that is 24 dB/km higher than otherwise. Therefore, to ensure an acceptable data error rate under all expected conditions, data is typically communicated over a wireless communication link at a relatively high power and at a relatively low rate. The amount of data required to be communicated over the wireless link, however, can vary widely over time and can vary independently of environmental conditions. In addition, wireless links, especially those operated at high power levels, can cause interference with other wireless links operating in the same geographical area. Thus, the wireless link can become a data communication bottleneck.
Therefore, a technique is needed for efficiently and cost effectively communicating data over a wireless link between Ethernet local area networks.
A wireless communication system is known having an intermediate frequency (IF) converter which is connected to a LAN and located inside the same building as the LAN. The IF converter modulates data signals from the LAN onto a first IF carrier signal. The first IF carrier signal is then routed to a roof-mounted unit via coaxial cabling. The roof-mounted unit then performs wireless transmission. Similarly, the roof-mounted unit receives wireless transmissions and provides a second IF carrier signal to the IF converter via the coaxial cabling. The IF converter demodulates the second IF carrier signal and provides the recovered data signals to the LAN.
This arrangement has a disadvantage in that the required coaxial cabling is relatively expensive in comparison to other types of cables. In addition, the IF converter increases the cost of the equipment required to be located inside of the building.
Therefore, what is needed is a technique for communicating data over a wireless link between local area networks which does not suffer from these drawbacks.